New bridge design offers high earthquake resistance at lower cost

A new study focuses on the implementation of new bridge designs that could provide earthquake resistance and highly reduce the cost of fixing a bridge after a failure.

The impact of an earthquake on a bridge structure can be critical. Partial or even total collapses of such structures have occurred in many cases resulting in massive infrastructure damage and casualties. For this reason, engineers are currently designing bridges with high safety standards using sophisticated computer models and experimental tests.

According to the Eurocode-8, a European standard that describes how to construct buildings when subjected to seismic loads, there are currently some basic requirements regarding bridge seismic design. The structure should remain stable after the occurrence of a strong earthquake (some partial failures may occur but a total collapse is considered unacceptable). Moreover, the bridge should remain fixable and repair works should be conducted readily. The sections that failed should be designed to absorb energy so that the vital parts of the bridge survive.

Nevertheless, a strong earthquake can still cause significant damage to a bridge and could result in an urgent need for repair works. The economic impact of such an incident is high (billions of dollars in the United States annually).

New concepts on bridge design have recently emerged and potentially guarantee seismic-resistant structures that could be repaired at lower costs if damaged. However, few of these concepts have been put to the test in actual case studies so that their potential could be evaluated.

Researchers from the University of Colorado, Boulder and the Texas A&M University carried out a thorough investigation of such a bridge design to assess its performance. The results of the study were recently published in the Journal of Structural Engineering.

According to Petros Sideris, co-author of the study and an Assistant Professor in the Zachry Department of Civil and Environmental Engineering at Texas A&M University, bridges are monolithic structures that perform great under their own weight and the weight of the vehicles that overpass them but, they are frequently damaged during earthquake incidents.

The research team designed a bridge consisting of columns that contain joint assemblies that replace the monolithic connections. The design is known as the "hybrid sliding-rocking bridge" and relies on reducing the seismic energy by allowing the joints to slide against each other.

A team of experts evaluated the observed damage from experimental tests on such columns. The columns were initially damaged in a controlled manner and were later fixed and re-tested. The behavior of the repaired columns was evaluated via computer models.

The findings suggest that the new design allowed the columns to undergo less damage compared to conventional monolithic columns even when subjected to a highly powerful earthquake load. Repair works were also much simpler and could be conducted faster without requiring any special technique.

Sources: Texas A&M University, Eurocodes